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A7689 - Assessment of Increased Expiratory Flows as the Earliest Pulmonary Function Test Abnormalities in Patients with Idiopathic Pulmonary Fibrosis and Interstitial Lung Diseases
Author Block: S. M. Alyami1, O. Moran Mendoza2; 1Division of Respiratory and Sleep Medicine, Department of Medicine, Queen's University, Kingston, ON, Canada, 2Medicine, Queens University, Kingston, ON, Canada.
Introduction:
The majority of interstitial lung diseases (ILD), including idiopathic pulmonary fibrosis (IPF), share a restrictive ventilatory defect as the common physiologic abnormality.
Low Dlco is traditionally considered to be the earliest abnormality on pulmonary function tests (PFTs) in patients with ILD/IPF. However, its measurement requires complex and expensive equipment, usually available only in Pulmonary Function Laboratories.
Rationale:
The increased elastic recoil in ILDs/IPF could result in increased expiratory flows. It is unknown, if high expiratory flows are the earliest abnormality on PFTs in patients with ILD/IPF.
Methods:
We reviewed the PFT results of incident cases of ILD/IPF seen at the interstitial lung disease clinic in Kingston, Ontario, Canada) between May, 2013 and December, 2017. The diagnosis of ILD/IPF was established as per current guidelines and supported by high resolution chest CT.
PFTs were done using standard equipment and according to American Thoracic Society recommendations. PFTs that were not acceptable or reproducible were excluded.
We performed a descriptive analysis of the type and frequency of abnormally high expiratory flows, defined as those above the 95% confidence limit of normal of the predicted value for gender, age, height and race among patients with normal FVC, TLC, and Dlco. We did the analyses for all patients with ILD, and separately for patients with IPF. We adjusted for emphysema, high airway resistance and body mass index by doing stratified analysis. We used SPSS® for the statistical analyses.
Results:
We analyzed PFTs of 289 patients with ILD, 88 (30%) of them with IPF. Among the 88 (30.4%) with normal forced vital capacity (FVC), total lung capacity (TLC) and carbon monoxide diffusing capacity (DLco), 31% had a high FEV1/FVC ratio, 5.7% high FEF25-75, 13.6% high FEF50, 2.3% high FEF75, and 4.5% high PEF. After adjusting for emphysema and high airway resistance, 58% had a high FEV1/FVC ratio, 6.5% high FEF25-75, 32.3% high FEF50, and 9.7% high PEF.
After adjusting for high BMI, among those with normal FVC, TLC and DLCO, 43% had a high FEV1/FVC ratio and 28.6% had a high FEF50. Results were very similar when this analysis was done only in patients with IPF.
Conclusion:
Abnormally high FEV1/FVC ratio is the earliest abnormality observed on PFTs in patients with ILD, including patients with IPF. This could allow identifying patients with ILD/IPF in the earliest stages of their disease with simple spirometry, leading to earlier diagnosis and treatment.